Device for cooling semi-conductors

ABSTRACT

The device serves for cooling electronic structural elements and has a cooling body and a metal base plate constructed as a part of the support of the structural element. The cooling body is arranged adjacent the base plate. A connecting element is arranged at least over areas between the base plate and the cooling body. The connecting element is at least partially constructed of a metal which has a melting temperature of at least 60° C. The connecting element is provided with a frame-like seal.

The invention relates to a device for cooling electronic structuralcomponents which includes a cooling body and a metal base plateconstructed as a part of a support of the structural element, whereinthe cooling body is arranged adjacent the base plate and wherein aconnecting element is arranged at least over certain areas between thebase plate and the cooling body.

Connecting elements of this type according to the prior art aretypically constructed as so-called heat conducting pastes. As a rule,such heat conducting pastes contain silicon and/or graphite. It is alsoalready known to use as connecting elements coated metal foils ornon-metal heat conducting elements. Generally, such connecting elementsserve for an improvement of the heat transfer between the electronicstructural component, typically a power semi-conductor element, and thecooling body.

From the field of constructing computers, it is also already known touse heat conducting foils. Such heat conducting foils have a meltingpoint in the range of above 58° C., typically in the range of 60° C.,and they are therefore not suitable for use in the field of powerelectronics because in that field frequently cooling body temperaturesabove 100° C. are encountered. Such cooling body temperatures may leadto the discharge of molten heat conducting foils and, consequently,there is the danger of short circuits.

It is the object of the present invention to construct a device of theabove-described type in such a way that an effective cooling ofelectronic structural elements is made possible even at higher coolingbody temperatures.

In accordance with the invention, this object is met by constructing theconnecting element at least over areas thereof of a metal which has amelting temperature of at least 60° C., and the connecting element isprovided with a frame-like seal.

Because of the selection of the above-mentioned melting temperature forthe metal and the use of a frame-like seal, it is possible even athigher cooling temperatures to utilize the very good heat transferbetween the structural element to be cooled, the metal connectingelement and the cooling body, and to still prevent the discharge ofliquefied metal when the melting point of the metal connecting elementis exceeded. The frame-like seal surrounds the metal connecting elementand rests against a support side, on the one hand, and a cooling body,on the other hand. In this connection, it is possible to provide eithera direct contact between the connecting element and the electronicstructural element; in accordance with other embodiments, it is alsopossible to position the electronic structural element on a metalsupport. It is essential for effective cooling that, starting from theambient temperature and prior to reaching a maximum operatingtemperature, the metal changes its state of aggregation.

To prevent molten metal from being discharged, it is proposed that theseal is constructed of a metal having a melting temperature above 200°C.

In particular, it is considered to construct the connecting element soas to be foil-like.

For compensating for increased volumes due to melting of the metal, itis possible to arrange at least one recess in the area of the connectingelement.

Moreover, it is also being considered to arrange at least one materialthickness reduction in the area of the connecting element.

It is also possible that the connecting element extends at least overareas thereof at a distance from the seal.

In accordance with another embodiment, it is provided that at least onerecess facing the connecting element is arranged in the area of theseal.

Moreover, it is also possible that the seal has in a direction extendingtransversely of the cooling body a greater height than a thickness ofthe metal foil.

In the drawings, embodiments of the invention are schematicallyillustrated. In the drawing:

FIG. 1 is a partial representation of a cross-section through a supportfor an electronic structural element which is in contact to a coolingbody through a metal connecting element;

FIG. 2 is a top view of a metal connecting element which is surroundedby a frame-like seal;

FIG. 3 is an embodiment modified in comparison to FIG. 2, with expansionspaces;

FIG. 4 is a further modified embodiment with a differently constructedexpansion space.

In accordance with the embodiment of FIG. 1, an electronic structuralelement 1, typically a chip, is positioned in the area of a support 2,typically a module. The support 2 has a metal base plate 3 which iscoupled through a connecting element 4 to a cooling body 5. The coolingbody 5 has for supporting its heat transfer to the ambient air coolingribs 6 which extend preferably in a direction which is modified ascompared to the structural element 1. Alternatively or as a supplementto the use of cooling ribs 6, it is also possible to use liquid cooling.In particular, it is intended to conduct an appropriate cooling mediumthrough assigned cooling ducts.

In accordance with the embodiment of FIG. 2, the connecting element 4 iscomposed of a metal foil 7 which is surrounded by a frame-like seal 8.In the mounted state illustrated in FIG. 1, the seal 8 is clampedbetween the base plate 3 and the cooling body 5 in order to ensure anecessary tightness.

In accordance with the embodiment of FIG. 3, one or more recesses 9 arearranged in the area of the metal foil 7. The recesses 9 ensure asufficient tightness of the frame 8 even when the metal foil 7 melts asa result of temperature influence and, as a result, a volume increase ofthe material of the metal foil 7 is caused. Thus, the recesses 9constitute expansion spaces in the event of a corresponding volumeincrease.

In accordance with the embodiment of FIG. 4, the metal foil 7 has asmaller thickness than a height of the seal 8. In this case, the heightof the seal 8 corresponds to a distance between the base plate 3 and thecooling body 5. The appropriate dimensioning of the seal 8 ensures thatabove the metal foil 7 an expansion space 10 is arranged which cancompensate for the corresponding volume increases of the material of themetal foil 7 in the case of liquefication. In particular, the metal foil7 can in a liquefied state compensate even for different distancesbetween the base plate 3 and the cooling body 5 which are caused by thefact that the base plate 3 assigned to the module typically has anarched shape.

A preferred use of the metal connecting element 4 according to theinvention takes place in connection with electronic structural elements1 which are constructed as power semi-conductors. They are used instationary as well as in mobile fields. Such mobile uses refer inparticular to power electric devices or components. The improved coolingeffect can be utilized for achieving different advantages. For example,it is possible to increase the power density as a result of the improvedcooling effect. Also, it is possible to facilitate an operation withincreased cooling agent temperatures and/or at increased ambienttemperatures. Generally, it is also possible to increase the servicelife of the structural elements 1 by reducing the operatingtemperatures.

When the structural elements are constructed as power semi-conductors,especially considered are realizations as IGBT or MOSFET. These may bepresent in discrete construction or in modular construction.

The metal connecting elements 4 according to the invention reduce theDIE temperature by about 4 to 6° K. Also, compared to a use of heatconducting pastes, a markedly reduced assembly work is required. Thereproducibility of the achieved cooling effect is improved and, as aresult, quality requirements of the production process can be safelyadhered to.

Used as material for the metal foil 7 are typically suitable alloys. Themelting point can be influenced through the composition of the alloy. Atypical alloy consists of indium, tin and bismuth. As necessary, indiumcan be replaced fully or partially by gallium.

Used as the material for the seal 8 can be tin, aluminum or copper or analloy which contains one or more of the aforementioned elements.

A typical thickness of the metal foil 7 is about 30 micrometers.However, also usable are metal foils 7 with a thickness in the range of20 micrometers up to 40 micrometers. A typical thickness of the seal 8is about 60 micrometers. Basically, also usable are material thicknessesin the range of 40 micrometers up to 80 micrometers.

The metal foil 7 used has during assembly a solid state of aggregation.In a conventional operation, the metal foil 7 has a liquid state ofaggregation and a discharge of the molten metal is prevented by the seal8. During each longer interruption of operation, the metal foil 7returns into the solid state of aggregation. The changes from the liquidstate into the solid state as well as from the solid state into theliquid state take place completely reversibly.

FIG. 5 once again illustrates the arched configuration of the base plate3 as already described above and the limitation of the expansion space10 resulting therefrom. After a liquefication of the metal foil 7, thelatter fills out the expansion space 10 and leads to a large areacontact between the base plate 3 and the cooling body 5 which is notillustrated.

1-8. (canceled)
 9. Device for cooling an electronic structural element,comprising; a cooling body; a metal base plate constructed as a part ofa support of the structural element, the cooling body being arrangedadjacent to the base plate; and a connecting element is arranged atleast over areas between the base plate and the cooling body, whereinthe connecting element is at least over areas thereof constructed of ametal which has a melting temperature of at least 60° C., and whereinthe connecting element is provided with a frame-like seal.
 10. Thedevice according to claim 9, wherein the seal is of a metal having amelting temperature above 200° C.
 11. The device according to claim 9,wherein the connecting element is constructed to be foil-like.
 12. Thedevice according to claim 9, wherein at least one recess is arranged inthe area of the connecting element.
 13. The device according to claim 9,wherein at least one material thickness reduction is arranged in thearea of the connecting element.
 14. The device according to claim 9,wherein the connecting element extends at least over areas thereof at adistance from the seal.
 15. The device according to claim 9, wherein atleast one recess is arranged in the area of the seal facing theconnecting element.
 16. The device according to claim 11, wherein theseal has a greater height in a direction extending transversely of thecooling body than a thickness of the metal foil.